A healthy teaching profession recognizes and rewards its excellent teachers, helps all teachers to grow, and when necessary counsels out its lowest performers.
Robust teacher evaluation systems provide teachers, schools, districts, and states with the means to this end. Diverse perspectives of teachers' impact on student learning, including objective measures, need to be considered. We know these systems are working if they can distinguish the full range of talent, not just a thumbs up or down, and serve as the engine for teachers' development. That's what robust means.